In the manufacture of automobiles, the upper and lower body modules are constructed separately and then permanently joined together by brazing. Thereafter, metallic solders are used to fill depressions located along the brazed seams. For example, metallic solder is applied to the groove where the back windshield of the upper module was brazed to the lower module. However, during the process of filling base metal braze joints, metallic solder will not adequately adhere to the brazed surfaces. Accordingly, a solder tinning paste or solder cream is incorporated as an underlay between the solder and the base metal surfaces thereby facilitating adherence of the solder and formation of the solder joint.
Solder tinning pastes or creams generally comprise a compound which prepares the surface by cleaning, fluxing and tinning such that the metallic solders will readily adhere thereto. That is, tinning pastes or creams generally are composed of a solder powder suspended within a liquid system which contains flux in a viscosity adjustment material. The quantity of the liquid system in relationship to the total prepared volume of solder tinning paste is defined by weight percentage. For example, an 80% solder tinning paste contains 80% metal in 20% non-metal liquid system.
It is important that the tinning paste conform to the requirements established by the particular process since flux and metal percentages can impact the reliability of the solder joint interconnection between the base metals. Accordingly, various tinning paste alloys are currently available for particular applications. One such solder tinning paste currently available and utilized in the automobile assembly process is an alloy composition containing 85% tin and 15% copper suspended in a zinc chloride flux. Specifically, the composition contains the following: tin-copper alloy, zinc chloride, muriatic acid, Stagum Type 1 (suspending agent), n. butyl Cellosolve and Sterox DJ (wetting agent). Although the tin-copper alloy composition is generally adequate as a solder tinning paste the composition contains impurities such as oxides and has a high workable melting point of 779.degree.0 F.
Furthermore, solder tinning pastes are used to fill dents inadvertently placed in the automobile during assembly of the car on the line. Also, some tinning paste compositions will not readily adhere on top of galvanized surfaces. Therefore, it would be desirable to provide a solder tinning paste easily spreadable at ambient temperature and having less impurities, a lower melting point and enhanced wetting and flowing characteristics at soldering temperatures comparable to the currently available tin-copper alloy paste.